1. Field of the Invention
This invention relates to the measurement of real transformers and inductors, and provides a method of modeling a magnetic component.
2. Description of the Prior Art
Man(H) is a single-valued function that represents the defect-free, or ideal, magnetization curve of a magnetic core and therefore it contains no hysteresis. A point on the Man(H) curve represents an anhysteretic state that is reached by demagnetizing the magnetic core sample under a constant magnitude of magnetic field. Each value of constant H yields a single value of B on the B-H plane once the demagnetization process is complete, where B and H are the magnitude of the magnetic flux density and the magnetic field, respectively. The material's magnetization may then be found from
                              M          ⁡                      (            H            )                          =                                            B              ⁡                              (                H                )                                                    μ              0                                -          H                                    Equation        ⁢                                  ⁢                  (          1          )                    where, M(H) is the magnitude of the magnetization, and μ0 is the permeability of free space.
The anhysteretic magnetization curve finds one of its primary applications in the mathematical modeling of magnetic cores where the I-V terminal characteristics of a magnetic circuit component are predicted from a model of the M-H relationship. Many spice-based simulators implement a form of the Jiles-Atherton model where the present value of M is predicted as an offset from Man(H). Multiple models exist for Man(H) as it has been shown that the magnetic anisotropy and texture of a material are solely modeled by a modification of the Man(H) equation. If a proper model of Man(H) is not applied in the modeling process, significant errors occur in the prediction of the M-H relationship.
A proper model of the M-H relationship of a magnetic core requires an accurate model of Man(H). However, temperature based models of Man(H,T) are needed to accurately model the temperature behavior of a magnetic core. Even in the isotropic model of Man(H), the Boltzmann statistics do not accurately model the curve's temperature behavior.
The major difficulty in the measurement of Man(H,T) arises from measuring the resulting anhysteretic state, or rather where on the M-H plane forms a point after the demagnetization process. This difficulty arises as a fundamental result of Faraday's Law. No voltage is induced by the core as it rests in the anhysteretic state, or rather no voltage is induced as the magnitude of M does not vary with time. As a result, the voltage induced as the core is at rest in its anhysteretic state is zero.
Ideally, the core must be set in its proper state and followed by a measurement of that state. Measurement of B should proceed after the demagnetization process is complete to ensure that B has come to its final value and to avoid reading any induction caused by the demagnetizing waveform. Therefore, magnetic sensors would be ideal to measure an anhysteretic state of a commercial core because magnetic sensors can measure static B fields. For magnetic cores, this requires the core to be cut, and the sensor to be inserted into the gap of the core. It is well known that such an alteration to the core changes the M-H relationship. Therefore, the introduction of a gap or modification of the core geometry would invalidate the measurement of the resulting B of the original core.
The known problems of commercial magnetic sensors, such as limited temperature range, temperature dependent output, and constant offset nulling, also further complicate the utilization of a magnetic sensor in the measurement process.
In the prior art, the method to measure an anhysteretic state began with soft magnetic samples being subject to vibration as a method of demagnetization. The material is placed experimentally into an anhysteretic state by applying a slowly decreasing alternating waveform with an applied bias. The point-by-point (ballistic) method can be performed to measure quasi-static curves and the anhysteretic curve. However, the basic problem of resolving a point on the anhysteretic curve by measuring an induced voltage still remains extremely difficult because a component of the flux which can change at a constant rate will not induce a voltage as a result of Faraday's Law. In practice, the point-by-point method for measuring quasi-static magnetization curves often produces different measurement results than the preferred continuous recording methodology often employed in most modern commercial systems. Another method to measure Man(H) is that the measurement of an anhysteretic state can be performed by measuring the change in the magnitude of B up to its saturation limit, where saturation is therefore used as a reference point to identify the magnitude of B. Caution must be exercised in using saturation as a reference due to the known difference in technical and true saturation. The magnitude of B continually rises during saturation due to the difference between technical and true saturation. This can make the application of saturation as a reference point somewhat arbitrary. One must assume that the initial point of reference as to where B begins is zero, or rather that the core has been ideally demagnetized. Given the existence of anhysteretic remanence, this is highly unlikely.
In all of these methods, the details of how the static components of the B field are resolved are not given, and they are believed to be neglected. A constant rising or falling B with respect to time will not induce a voltage as a result of Faraday's Law. A B waveform that is maintained at a constant offset from zero will also not induce a voltage.
As discussed above, modern power conversion systems use components that exhibit very nonlinear behavior as a result of their magnetic field (B-H) characteristics.
Apparatuses of the prior art cannot measure the full B-H loop for a magnetic core under applied bias conditions. The various apparatuses also cannot measure static non-time varying B-fields, which are required to be measured when measuring the anhysteretic magnetization curve. This is a result of the fundamental measurement method relied on by these apparatuses.
There are two categories of equipment presently used. The first category uses a winding of wire around a magnetic core to measure the core's flux, and the second category uses a sensor. To use a sensor, a magnetic core must be cut and a sensor must be inserted inside the gap of the core. This changes the B-H properties of the core. The benefit of using a sensor is that it can sense a static or non-time varying B-field. Before this equipment was invented, a simple winding of wire around the core could not be used to measure a static or non-time varying B-field. This is the only presently known type of equipment that can measure the B-H relationship under applied bias as well as the true anhysteretic magnetization of a magnetic core, while avoiding cutting the core.
Further, the design of complex power conversion systems has been hampered by a lack of the ability to properly predict the terminal characteristics of magnetic components.
There is no method currently available to directly measure the complex magnetic core properties accurately enough to permit accurate device and system design.